In the treatment of some diseases or defects associated with a patient, it has been found necessary to access specific targets within a patient. In the treatment of some diseases of or defects of human beings, it has been found necessary to access specific portions of the brain. Currently there are several methods for inserting surgical and observational instruments into a patient's brain.
U.S. Pat. No. 3,055,370 issued to McKinney et al. shows one currently used method for placing a surgical instrument to access a specific portion of the brain. The surgical instrument of the U.S. Pat. No. 3,055,370 patent includes a ball which has a bore. The direction of the bore can be changed. The instrument has an elongated tube of a specific length. A stylet is inserted within the tube to access the globus pallidus and perform a pallidotomy. An opening or burr hole is made in the skull at a specific landmark on the skull. Next, X-rays are taken in the fore-and-aft (AP) and lateral positions, and the line of the bar is projected downwardly by a ruler both in the fore-and-aft (AP) and lateral positions, so that the direction of the needle can be determined before it is inserted. When the direction of the longitudinal axis of the tubular member is determined to be satisfactory, a holder is threaded further into a tap to force a surface against a ball and lock a tubular member into place. Alignment of the trajectory is not measurable along a specific line occurring at the intersection of two planes. Alignment is dependent on placement of the burr hole at a specific location to determine one plane. X-rays are used to determine another plane-based use of common landmarks on the skull. The end result is that an educated guess is being used to position the stylet at the globus pallidus for the pallidotomy. One shortcoming with the method of using X-ray imaging to direct a surgical or observational instrument, is that many of the destinations within a patient are not viewable via X-ray. Another shortcoming relates to the slight shifting of intracranial contents, once a burr hole is placed and the dura and arachnoid are penetrated. Once cerebrospinal fluid is released via the burr hole, the intracranial contents (i.e. brain) may shift one or more millimeters. In such a case, the calculated trajectory is no longer accurate. Hence, there is an inherent inaccuracy with the described scheme.
Several other methods are also used to place instruments, catheters, or observational tools into patients. Like the method discussed above, most surgical procedures are performed through craniotomy flaps or craniotomy burr holes. A burr hole is an round opening in the skull having a diameter of about 14 mm. The diameter is a standard length in most parts of the world. Currently, the Europeans use a slightly different standard diameter of about 15 mm. Needles or probes are typically passed through the burr hole into the brain using framed stereotaxy, frameless stereotaxy or freehand without stereotaxy. Many instruments used for doing various operations attach to the burr hole. Many use an outside thread that grips the inner diameter of the burr hole.
The freehand method depends very heavily on the knowledge and judgment of the surgeon. In the freehand method, the surgeon determines the insertion point with a couple of measurements from a known landmark. The surgeon then looks at the measured point, makes adjustments, determines the angle of insertion and then inserts the surgical instrument or tool.
In framed stereotaxy, a ring frame is mounted to the patient's skull by multiple (typically three or four) pins or screws. This ring frame is used to determine a three dimensional data set. From this data set, Cartesian coordinates are calculated for both the lesion, the location of the pins or screws, and the fiducial marks on the frame. The ring frame fits into a large frame. A large frame is then attached to the patient in the operating suite. The large frame provides known positions and guides the surgical or observational instruments. The large frame is used to position the instrument to be introduced into the patient through a burr hole so that it intersects the target. In frameless stereotaxy, the ring frame is replaced with several markings on the patient's skull which can be used to determine several known positions. The large frame is replaced by a camera. The camera is usually infrared or some such device. Multiple sensors readable by the camera are placed on the instrument. For example, the surgical instrument or tool is provided with one or more light emitting diodes ("LEDs") which are tracked by the camera. The position of the surgical instrument can be calculated from the information from the LEDs on the surgical instrument or observational tool.
U.S. Pat. Nos. 4,955,891 and 4,805,615, both issued to Carol, each discuss the use of stereotaxy surgery with computerized tomographic ("CT") scanning. CT scanning is used to determine the exact position of a lesion or specific portion of the brain. After the exact position of the lesion or specific portion of the brain is determined, a phantom fixture is set up. The phantom fixture replicates the position of the ring frame on the patient. A phantom target is set up. The phantom fixture and target are typically determined outside the operating suite. Within the operating suite, the instrument can then be positioned on the phantom fixture such that it intersects the target. The information from the phantom fixture can then be used to initially position the instrument in the operating suite. Most procedures require forming a burr hole in the patient's head. Loss of fluid from the burr hole results in a shifting of the contents of the cranial cavity. The burr hole is typically made in the operating suite after the phantom frame and target have been set up. As a result, a subsequent CT scan is necessary especially in the case when the target is small, thereby requiring accurate placement of the instrument.
U.S. Pat. No. 4,998,938 issued to Ghajar et al. shows another surgical device for facilitating the insertion of an instrument into a patient's cranial cavity through a burr hole. The device includes a guide having an end configured to pass into the burr hole. There is a separate locking member. A body member includes alignment markings to help with insertion of a catheter or stylet. Unlike U.S. Pat. No. 3,055,370, there is no movable member for adjusting the path of the guide.
The methods currently in use all have a number of shortcomings. One of the shortcomings is that all of the techniques require initially making craniotomy flaps or craniotomy burr holes in the patients skull or body. A burr hole of about 14 mm is made in the skull. Needles or probes are typically passed through the burr hole into the brain during a typical procedure, such as a biopsy or laser ablation of a tumor. The burr hole formed is large and it takes a fair amount of surgical time to make. In addition to the surgical time, the forming of the burr hole results in shifting of the contents within the cranial cavity. It would be advantageous if a surgical tool would allow surgical procedures to be performed without the formation of a burr hole. In addition, it would be advantageous if tools that attached or required a burr hole could be adapted so that the surgical procedure would not require formation of the burr hole in the patient's skull. The formation of a burr hole is a time consuming portion of an operation.
Most of the techniques currently used to place a surgical instrument or observational tool within a patient employ a limited amount of accuracy. In particular, current framed, frameless, and freehand methods compute or predict trajectories on the basis of imaging data or anatomic landmarks that do not account for the slight, but real shifting of the brain upon opening the cranium and meninges to the level of the subarachnoid space. This inherent inaccuracy inherently limits the success of these various methodologies. In other words, these systems do not use any means of updating the data files to include data obtained following the placement of a surgical burr hole and opening of the meninges. In addition, all the methods require large amounts of judgment on the part of the surgeon placing the surgical instrument or tool, and in particular, offer no direct feedback on the success or failure of the trajectory to reach the target. Very few of the techniques use an imaging or scanning apparatus to aid in the placement of the surgical instrument or observational tool. The only one that does requires a phantom frame and target to be set up to simulate the real geometry. In short, none of the apparatuses appear to use an imaging or scanning apparatus as extensively as they could be used to minimize the time and effort needed to accurately place a surgical instrument into a patient, and to offer immediate data on the success or failure of the trajectory to reach the target. It would be advantageous if more accurate methods could be developed which could use either MR or computerized tomographic ("CT") scanners. Both MR or CT scanners are widely available worldwide. Even though CT scanning equipment has the disadvantage of patient exposure to x-radiation, a method for accurate placement of an instrument using CT scanning equipment would be even more widely available to patients around the world than a similar MR method.